1. Field of the Invention
This invention relates to the field of pectin gels and more particularly, to such gels based on low methoxyl pectin.
2. Description of the Prior Art
For many years, gelatin desserts have enjoyed universal popularity due to a combination of appealing taste and texture characteristics and relative ease of preparation. Typically, a quantity of dry gelatin mix is dissolved in a given amount of hot water to provide complete dissolution of the gelatin, a like amount of cold water is then added to the dissolved mix to satisfy the full water requirements of the mix and the resulting warm dissolved gelatin solution is chilled for several hours to allow the gelatin to set. There has long been a desire to provide a gelatin dessert in quick-gel form. Such a product would not have to be prepared hours in advance as with the gelatin compositions now available, but could be made ready for consumption within minutes and in response to unanticipated needs. However, the basic physical and chemical properties of gelatin, a protein obtained from animal skin, tendons, ligaments, bones, etc., has so far resisted fully successful attempts toward instantization.
Pectin has been the focus of many studies designed to provide cold water-soluble quick-set edible gels. Pectin is a gellable substance, derived from fruits and vegetables which structurally is partially methoxylated polygalacturonans built up from D-galacturonic acid units forming long chain-like molecules. The pectin is available in two forms, each of which gels by a different mechanism, that is a high methoxyl (HM) type having a degree of methoxylation (DM), or ratio of methoxylated galacturonic acid groups to total acid groups of 50% or above, and a low methoxyl (LM) type having a DM of less than 50%. One method of producing an LM pectin involves reacting methoxyl groups with ammonia to form amide groups. The resulting pectin usually contains from about 2.5 to 4.5% methoxyl groups by weight as compared to the HM pectin which generally contains from 8-14% methoxyl groups by weight. HM pectin requires a sugar or soluble solid content of approximately 55% by weight or higher and a pH of about 3.0-3.2 to achieve set. When the methoxyl ester content of LM pectin goes below about 7 %, the pectin loses its ability to form sugar-acid gels as in the HM pectin, but acquires the ability to form gels through crosslinking of the carboxyl groups on neighboring adjacent pectin molecules or chains in the presence of polyvalent calcium ions. However, the very ease with which LM pectin undergoes irreversible gel formation in the presence of polyvalent calcium ions has inhibited its widespread use in the food industry. The calcium salt which provides the ions effecting gel formation dissolves and ionizes in cold water at a considerably faster rate than the rate of dissolution of the LM pectin causing premature gelation of the pectin before all the pectin has had an opportunity to dissolve. The resulting product will either fail to gel, or if a gel is formed it will be non-continuous and possess an entirely unacceptable gritty or lumpy texture. As a result, in comparison to HM pectin, only a small amount of LM pectin is now being used in food products. Due to its functional properties and its ability to set in the presence of polyvalent calcium ions and without the addition of sugar, LM pectin is used in a variety of food products requiring a gelled texture such as fruit toppings, ice cream and novel dessert preparations. But because of its high calcium ion sensitivity, poor solubility and difficult method of preparation, LM pectin has thus far enjoyed only limited use.
Attempts have been made to overcome the problem of premature gelation associated with the LM pectin by using slowly or slightly soluble calcium salts (e.g., calcium phosphate or sulfate) in the presence of monovalent metal ions such as those of sodium (e.g., provided by sodium citrate) which can retard the rate of cross-linking sufficiently to permit dissolution of the pectin as proposed in Pectin L.M. (Sunkist Growers Inc., 1953). U.S. Pat. No. 2,701,767 describes the coating of the calcium salt particles to reduce their rate of dissolution as well as co-drying of the pectin with a monovalent metal salt such as sodium citrate to delay gel formation. U.S. Pat. No. 2,559,338 provides a method for ensuring the solution of at least a substantial quantity of LM pectin before appreciable solution of calcium salt occurs by dissolving a soluble edible acid such as citric, malic, tartaric, fumaric or ascorbic acid with each calcium salt particle at the same time and place in the gel-forming solution. Methods of increasing the rate of solubility of LM pectin in cold water to approach that of the calcium salt are described in U.S. Pat. Nos. 2,673,157 and 2,856,288. According to these methods, the pectin is co-dried with sugars such as lactose, sucrose, dextrose, etc., to accelerate dissolution.
U.S. Pat. No. 3,041,179 provides an HM pectin (60-73% DM) dry mix containing a dispersant, fruit acid and adipic acid. U.S. Pat. No. 3,140,186 discloses an HM pectin (72-75% DM) dry mix combined with adipic acid for improved flowability. The gel composition of U.S. Pat. No. 3,367,784 employs an LM pectin (25-35% DM), a source of calcium ions, a source of ions of another alkaline earth metal, preferably magnesium, an edible acid, buffer or solubilizer, flavor, color and preservative. The gel is prepared by dispersing a first component containing the pectin in cold water and heating the water to complete dissolution of the pectin, dissolving a second component containing the source of calcium ions in hot water and combining the two hot solutions. Other gel-forming LM pectin compositions are described in U.S. Pat. Nos. 2,524,416; 2,784,099; 2,809,893; 2,809,894; 2,824,007; and 2,910,365.
None of the foregoing pectin gel dry mix compositions are provided as a single packet system which can be conveniently and rapidly converted to a smooth gel of appetizing flavor and texture characteristics by the dissolution of the same in cold or ambient temperature water with varying water hardness.